This invention relates to systems and methods for processing blood, e.g., for filtration, pheresis, or other diagnostic or therapeutic purposes.
There are many types of continuous and intermittent blood processing systems, each providing different therapeutic effects and demanding different processing criteria.
For example, hemofiltration emulates normal kidney activities for an individual whose renal function is impaired or lacking. During hemofiltration, blood from the individual is conveyed in an extracorporeal path along a semipermeable membrane, across which a pressure difference (called transmembrane pressure) exists. The pores of the membrane have a molecular weight cut-off that can thereby pass liquid and uremic toxins carried in blood. However, the membrane pores can not pass formed cellular blood elements and plasma proteins. These components are retained and returned to the individual with the toxin-depleted blood. Membranes indicated for hemofiltration are commercially available and can be acquired from, e.g., Asahi Medical Co. (Oita, Japan).
After hemofiltration, fresh physiologic fluid is supplied to toxin-depleted blood. This fluid, called replacement fluid, is buffered either with bicarbonate, lactate, or acetate. The replacement fluid restores, at least partially, a normal physiologic fluid and electrolytic balance to the blood. Usually, an ultrafiltration function is also performed during hemofiltration, by which liquid is replaced in an amount slightly less than that removed. Ultrafiltration decreases the overall fluid level of the individual, which typically increases, in the absence of ultrafiltration, due to normal fluid intake between treatment sessions.
Following hemofiltration, fluid balancing, and ultrafiltration, the blood is returned to the individual.
One aspect of the invention provides hemofiltration systems and methods that employ an extracorporeal circuit to circulate blood from an individual through a hemofilter to remove waste. The extracorporeal circuit includes a blood line coupled to the hemofilter and adapted to draw blood from the individual. A blood pump conveys blood through the blood line from the individual into the hemofilter. A waste removal line communicates with the hemofilter. A waste removal pump conveys waste fluid through the waste removal line at a waste removal rate. A sensor in the waste removal line senses waste fluid pressure. The systems and methods adjust the waste removal rate to maintain waste fluid pressure at a predetermined set value. In this way, the systems and methods optimize removal of waste fluid by the hemofilter.
In one embodiment, the predetermined set value is a positive value not significantly above zero.
In one embodiment, the blood line is free of an arterial blood pressure sensor.
In one embodiment, the blood pump is operated to achieve an essentially fixed blood flow rate.
According to another aspect of the invention, the blood pump conveys blood through the blood line from the individual into the hemofilter at a blood flow rate. A sensor is located in the blood line to sense blood pressure. In this arrangement, the systems and methods adjust the blood flow rate to maintain blood pressure at a predetermined set value.
In one embodiment, the systems and methods generate an alarm output based upon variance between sensed blood pressure and the predetermined set value. The alarm output terminates operation of the blood pump.